1. Field of the Invention
The present invention relates to enhancing the service life of high-pressure pumps and particularly the valve heads of multi-piston pumps. More specifically, this invention is directed to valve heads for pumps and especially to armoured valve heads which include fluidic compensators to minimize component wear. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well-suited for use in and as a valve head for multi-piston high-pressure pumps. Such pump valve heads include a housing connected to each pump cylinder and having, oppositely disposed from one another with respect to the pump cylinder, intake and pressure connections. The intake connection includes a fluid intake line and an inlet valve. The pressure connection includes a pressure or discharge line and a pressure or discharge valve. The formation of cracks in the components of such pump valve heads, due to high stresses in the region of the pump cylinder, is a well-known and persistent problem in the art. The reason for the formation of such cracks, i.e., the cause of the metal fatigue in the components of the valve heads for high-pressure pumps, will be discussed in further detail below.
Several attempts have previously been made to address the problem of crack formation in pump valve head components. Thus, by way of example, published British Patent Application No. 1,027,934 shows a pump valve head wherein the valve head housing is provided with a central bore and, in both the intake connection and the pressure connection, a cross-bore branching off the central bore is provided. In the arrangement of G.B.-A No. 1,027,934 a manifold bushing is fitted and braced in the central bore and bushings which define the pump intake port and the pressure or discharge port are fitted and braced in the cross bores. The bushings which define the intake and pressure ports respectively surround the inlet valve and pressure valve. The manifold bushing is designed to function as an armoured bushing and is fitted into the central bore of the valve head housing in such a manner as to define a sealed-off annular gap. The bushing which surrounds the pressure valve is provided with at least one radial passage through which the pressurized fluid discharged from the pump cylinder may flow. An arrangement of the type disclosed in G.B.-A No. 1,027,934 has been found to afford inadequate protection against stress crack formation, particularly in the region of the pressure and inlet valves.
Published German Patent Application No. 2,940,606 depicts another approach to protection of all highly-stressed pump head zones against crack formation. In the technique of this German Application the bushings surrounding the pressure and inlet valves are formed as armoured bushings and are fitted into the respective cross-bores in such a manner as to define annular spaces. Fluid communication is established, via a bore in the bushing surrounding the pressure valve, between a receiver region downstream of the pressure valve and the annular gap surrounding the pressure-side bushing. The latter annular gap is, in turn, connected via passages with the annular gap around the intake-side armoured bushing. Both annular gaps are sealed so as to prevent discharge of pressurized fluid provided thereto to thereby form a pressurized fluid jacket which effectively surrounds all of the armoured bushings. A pump head design of the type disclosed in published German Application No. 2,940,606 is known in the art as a hydrostatically armoured pump head.
Field tests have shown that, particularly in the case of multi-piston pumps which supply fluid at a pressure in excess of 1,300 bar, the mechanical connections established between of the internal parts, as provided by conventional axial threads, is inadequate on the intake side of the pump head even in the case of previous "hydrostatically armoured" pump heads. That is, in the case of valve heads of the type shown in published German Application No. 2,940,606, the components forming the valve head on the intake side are held in their desired relationship by means of manually applied axial thread force. When a working pressure of approximately 1,300 bar is exceeded, elastic deformations occur and these deformations are cyclic, i.e., occur in time with pump surges. These elastic deformations cause the formation of clearances between the stacked components of the structural valve elements arranged on the intake side. When the forces are relieved, and thus the clearances resulting from elastic deformation disappear, the components of the valve head impact against one another with considerable force and, in prolonged operation, damage resulting from metal fatigue will occur.